Browsing by Author "Chang, Li-Wei"

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On Different-Dimensional Deployment Problems of Hybrid VANET-Sensor Networks with QoS Considerations
(2017-02-01)
Lin, Chun-Cheng
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Chen, Peng-Chung
;
Chang, Li-Wei
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工業工程與管理學系
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Department of Industrial Engineering and Management
To enhance vehicular ad hoc networks (VANETs) with the ability to detect road conditions, hybrid VANET-sensor networks (HVSNs) additionally deploy a large number of wireless sensors on road sides, so as to provide a safer driving environment. Most of the previous works on network deployment problems considered too simplified problem settings, and few of them focused on deploying HVSNs. To meet more practical requirements, this paper investigates the problem of deploying roadside units (RSUs) to serve sensors on three different-dimensional road settings (i.e., a one-dimensional road, a road represented as grid points, and a dense network environment) in HVSNs with two objectives (i.e., to minimize the total distance and the total number of hops from sensors to their respective closest RSUs) and two QoS constraints (i.e., for maximal number of hops and capacity). Achieving the two objectives can effectively decrease the probability of transmission interference and lead to shorter transmission time to inform drivers of unexpected events. Since the optimal deployment problems for a grid road and a dense HVSN cannot be solved analytically, this paper creates mathematical programming models for the problems, and further proposes an improved harmony search algorithm. By simulation in different-size instances and statistical analysis, the proposed approaches show promising performance in solving the problems.
On Different-Dimensional Deployment Problems of Hybrid VANET-Sensor Networks with QoS Considerations (April, DOI 10.1007/s11036-016-0698-4, 2016)
(2016-10)
Lin, Chun-Cheng
;
Chen, Peng-Chung
;
Chang, Li-Wei
;
工業工程與管理學系
;
Department of Industrial Engineering and Management
Performance analysis of S-MAC protocol
(2013-09-01)
Chang, Li-Wei
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Huang, Yueh-Min
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Lin, Chun-Cheng
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工業工程與管理學系
;
Department of Industrial Engineering and Management
Wireless sensor networks have been developed in the way of higher speed, more stability, and more energy efficiency in recent years. Because most wireless sensors are powered by energy-constrained batteries, efficient energy consumption plays the most important role in the design of wireless sensor networks. For energy efficiency, aside from economizing the use of power in the sensor hardware, extensive research efforts have been dedicated towards designing energy-efficient protocols in the MAC layer. Among them, the S-MAC (sensor medium access control) protocol proposed a combined scheduling and contention scheme to decide when to put sensors into the sleep state for saving energy. In this paper, we further conduct the performance analysis of S-MAC protocol, in which the mathematical equations for the saturation throughput analysis of S-MAC protocol are derived, and then simulation data are substituted into those equations and the S-MAC protocol, respectively. The simulated throughput results have shown that our derived equations can capture the characteristics of the S-MAC protocol. In addition, as compared with the conventional carrier sense multiple access/collision avoidance protocol, the simulation results show that the S-MAC protocol performs better in terms of power consumption, delay, and collision rate. Copyright (c) 2013 John Wiley & Sons, Ltd.